Birthstone Guide: Peridot for Those Born in August

Lily Faber FGA, gemmology and diamond tutor at Gem-A unveils the striking tones of peridot, the August birthstone; a fitting beauty of nature to compliment the vibrant and zesty 2017 Pantone Colour of the year, 'Greenery'.

Peridot is the birthstone for August and is known for its rich, green colour. It is one of the few gems that comes in only one colour (green), and its name is thought to come from the Arabic word ‘faridot’ which translates to ‘gem'.

Peridot is a transparent gem variety of olivine. Coloured by iron, it comes in a range of greens from yellowy-green to brownish-green. It also has a slightly oily or greasy lustre, but don’t let that description put you off!

With its distinct olive-green hue that is the embodiment of long, summer days, some believe that peridot can bring happiness, luck and prosperity while calming anger, conquering fear and protecting one from evil spirits.

Formed in the earth’s mantle, this gem makes its way to the surface via volcanic eruptions and is found in ancient lava beds. Occasionally, it can also come from outer space! A special type of meteorite called a pallasite meteorite sometimes contains peridot within its iron-nickel matrix. If you slice the meteorite open, it will reveal a smattering of transparent to translucent gems.

Zabargad Island, (St. John’s Island) in the Red Sea off the coast of Egypt, is believed to be the earliest known source for peridot. Centuries ago, the Greeks called this island Topazios, which was also their name for peridot. Later, this island was mined for peridot to fill the coffers of Egyptian kings and anyone who tried to set foot on the island at that time was threatened with death.

It has been said that many of Cleopatra’s emeralds, a favourite gem of hers, were actually peridot. Strangely, the ancient Romans called peridot the ‘Evening Emerald’ because they believed that its bright green colour could only be seen at night, which is clearly not the case!

Other localities include Myanmar, Pakistan and the Peridot Mesa in the San Carlos Apache Native American Reservation in Arizona, USA.

This is a brittle stone with a hardness of 6 ½, which leaves it vulnerable to chips and scratches. Care should be taken when set in jewellery, especially rings. Perfumes, hairspray and make-up can also damage the stone, so spritz your perfume prior to draping yourself in peridots.

Common inclusions are lily pads, which consist of crystals, typically chromite, and are surrounded by curved stress cracks. Mica flakes can sometimes give a brownish tinge to the gem, and needle-like ludwigite inclusions are also seen.

Lilypad inclusions. Image by Pat Daly FGA, Gem-A.

Mica inclusions. Image by Pat Daly FGA, Gem-A.

Ludwigite and vonsenite inclusions. Image by Pat Daly FGA, Gem-A.

A characteristic feature that can help differentiate peridot from emeralds is its high birefringence of 0.036, within an RI range of 1.65 to 1.69. This causes the effect of doubling of the inclusions and facet edges. You can often see this doubling with a loupe or even with the unaided eye if the stone is big enough.

Doubling of inclusions and facet edges observed peridot (note: this image is not out of focus). Image by Pat Daly FGA, Gem-A.

The most prized peridots are those of larger size, with a rich, ‘oily’ green colour and few inclusions.

While this stone has gone in and out of fashion over the years, I encourage you to think of peridot for your next piece of jewellery not only for its gorgeous colour, but also for its interesting and varied history.

Guy Lalous ACAM EG presents us a historical review, and an updated overview, of the Brazilian coloured stone industry. His latest Journal Digest from Gem-A’s Journal of Gemmology (Winter 2017. 35.8) also examines the effects of China’s emergence as a consumer market on Brazil’s gem industry.